Use of radiolabeled target-seeking biologically active molecules (hereinafter referred to as BAMs), especially antibodies and other proteins, for diagnostic and therapeutic purposes is a highly active field. For a discussion of such radiolabeling, see Eckelman et al., Radiolabeling of Antibodies, Cancer Research, 40: 3036-3042 (1980) and Sfakianakis et al., Radioimmunodiagnosis and Radioimmunotherapy, J. Nucl. Med. 23: 840-850 (1982). The most widely used means of radiolabeling antibodies has been direct iodination with I-131, I-125 or I-123. However, these radionuclides have certain dosimetric and imaging disadvantages. Certain metallic radionuclides such as Tc-99m and In-111 are more suitable for scintigraphic imaging. However, it has heretofore been difficult to attach these metallic radionuclides directly to most BAMs because generally there is insufficient affinity between the radionuclide and the BAM. Further, in some cases where such attachment has been possible, the attachment of radionuclide sometimes results in partial or complete loss of the biological activity of the BAM.
For these reasons, it has been proposed by many in the art to radiolabel BAMs with metallic radionuclides by covalent conjugation using a metal chelating agent. For example, Khaw et al., Science 209: 295-297 (1980) discloses antibodies to cardiac myosin labeled with In-111 diethylenetriaminepentaacetic acid (DTPA) and use of the labeled antibodies to image for myocardial infarction. Krejcarek et al., Biochem. Biophys. Res. Commun. 77: 581-585 (1977) discloses use of DTPA to label proteins such as human serum album (HSA) with metal radionuclides. Pritchard et al., Proc. Soc. Exp. Biol. Med. 151: 297-302 (1976) discloses conjugation of antibodies to various agents capable of chelating In-111, such as transferrin, D-penicillamine and deferoxamine. Yokoyama et al., European Patent Application No. 35,765, published in 1981, discloses deferoxamine as a bifunctional chelator for radiolabeling various BAMs, including proteins (e.g., HSA, urokinase, fibrinogen), antibiotics (e.g., "Bleomycin", "Kanamycin") hormones, saccharides and fatty acids. Haber et al., European Patent Application No. 38,546 published in 1981, discloses DTPA, ethylenediaminetetraactic acid (EDTA) and ethylenediamine as bifunctional chelators for radiolabeling proteins, including antibodies, antigens and antibody fragments. Yokoyama et al., U.S. Pat. No. 4,287,362 issued in 1981 discloses 3-carboxy-2-oxopropionaldehyde bis(N-methylthiosemicarbazone) (OPBMT) and analogs as bifunctional chelating agents for radiolabeling proteins. Sundberg et al., U.S. Pat. No. 3,994,966, issued in 1976, Meares et al., U.S. Pat. No. 4,043,998 and Leung et al., Int. J. App. Radiation and Isotopes 29: 697-692 (1978) disclose bifunctional EDTA analogs such as 1-(p-benzenediazonium)-EDTA and 1-p-aminophenyl-EDTA for protein labeling. Paik et al., J. Radioanal. Chem. 57: 553-564 (1980) discloses an azo derivative of DTPA called DTTA-azo-imidate as a bifunctional chelator and its use to label HSA with In-111. Each of the bifunctional chelators heretofore described, however, has generally been designed to coordinate a specific metallic radionuclide. It would, therefore, be desirable to develop a chelator capable of coordinating a variety of metallic cations, and capable of conjugation with BAMs, while retaining the biological activity of the BAMs.
Further, current intravascular radiographic contrast agents are based upon iodinated aromatic compounds. These compounds, however, are often found not to be physiologically tolerable at useful concentrations. Therefore, it would be desirable to develop physiologically compatible alternatives to such iodinated compounds.
Also, in the rapidly developing field of nuclear magnetic resonance (NMR) imaging, useful contrast agents would be valuable, particularly if capable of conjugation with BAMs. Brasch (Radiology, 147: 781-788, (1983)) in his review of methods of contrast enhancement for NMR imaging, notes among criteria for the "ideal" contrast enhancer, that the compound should have strong NMR activity at low concentrations, be non-reactive in vivo, and should be non-toxic in diagnostic doses.